1. Technical Field
The present invention relates to physiological sound examination devices. The present invention particularly relates to a physiological sound examination device which supports estimation of a state of a living body by measuring a physiological sound that propagates through the living body and calculating plural physiological sound characteristics.
2. Background Art
In a hospital or the like, a doctor listens to a physiological sound of a patient, such as heart sound or lung sound, using a stethoscope to make a diagnosis. The diagnosis by auscultation is based on a subjective evaluation of the doctor. On this account, skill is required to make a correct diagnosis.
The lung sound refers to all sounds, except for sounds coming from the cardiovascular system, generated by the motion of breathing in the lung and thorax regardless of whether normal or abnormal. Moreover, the lung sound is divided into a breath sound and an adventitious sound. The breath sound refers to a physiological sound whose source is airflow occurring in the respiratory tract by breathing. The adventitious sound refers to an abnormal sound, such as wheezing or pleural friction rub, caused in a pathological state. The sound source of breathing is thought to be generated in the respiratory tract which is relatively large.
In the conventional diagnosis, a diagnosis support for lung diseases is provided by performing signal processing of a lung sound. In the diagnosis support for lung diseases, an adventitious sound is detected to estimate a state of the disease. However, an objective index for the disease has not yet been established.
Pneumothorax is one of lung diseases. Pneumothorax is an air space formed between the lung and the chest wall, and appears as a decrease in breath sound intensity in physical presentation. A method of detecting a state of pneumothorax has been disclosed (see PTL 1, for example). More specifically, in this method, a sound wave is emitted by a speaker into the mouth and the trachea so that the emitted sound wave propagates through the body of the patient, and then the propagated sound wave is measured on the chest wall for signal processing. According to PTL 1, the state of pneumothorax is detected by calculating a transfer characteristic from the sound wave to be emitted and the sound wave measured on the chest wall.
Moreover, as a method without emitting a sound wave by a speaker, a method of analyzing the lung sound measured on the chest wall is disclosed (see PTL 1, for example). According to PTL 1, frequency conversion is performed using a lung sound signal measured on the chest wall, and an energy ratio between a low frequency band component and a high frequency band component is calculated. In this way, a respiratory state can be detected.
Here, for making a respiratory diagnosis, the doctor listens to the lung sound by placing a stethoscope on different positions of the body. A device which includes, in order to detect a measurement position of the lung sound, an acceleration sensor in a sensor for measuring the lung sound has been disclosed (see PTL 2, for example). According to PTL 2, output values of the acceleration sensor are integrated to calculate a moving distance of the sensor, so that the measurement position of the lung sound can be automatically detected.
Furthermore, when a patient is in a remote area, a person other than the doctor places a microphone on a predetermined position of the body of the patient to measure the physiological sound and then transmits the measured physiological sound via a communication line to the doctor who thus listens to the physiological sound signal to make a diagnosis. In order for the doctor in a remote area to be able to make a diagnosis even when the microphone is not placed on the predetermined position of the body of the patient, a device whereby more than one microphones are placed on the body of the patient to help the doctor make the diagnosis has been disclosed (see PTL 3, for example). According to PTL 3, a weighted sum is calculated using acoustic signals received from the microphones, so as to simulate an acoustic signal corresponding to a position where no microphone is placed. In this way, a diagnosis made in a remote area is supported.